In 100 ml sample of hard water, 100 ml of 
Na 2 CO 3 solution was added and the mixture was boiled and filtered. The filtrate was neutralised with 60 ml of (N/50) HCl. If the density of hard water sample was 1 gm/ml, determine the permanent hardness of given hard water sample in ppm of CaCO 3 in nearest possible integers.
Text Solution
Verified by Experts1
(1) Given Data:
Volume of hard water sample 
(since density is 
Volume of Na 2 CO 3 solution added 
Volume of 
used for neutralization 
(2) Concepts Involved:
Permanent hardness of water is due to the presence of calcium and magnesium ions, typically measured by complexometric titration using EDTA (ethylenediaminetetraacetic acid).
EDTA reacts with calcium and magnesium ions to form stable complexes, allowing the determination of their concentration.
(3) Steps to Solve:
Step 1: Titration with Na 2 CO 3
Na 2 CO 3 reacts with 
and 
ions in hard water to form insoluble carbonates:
This removes temporary hardness due to carbonates.
Step 2: Filtration
Boiling and filtration remove the precipitated 
and 
.
Step 3: Neutralization with 
Remaining 
and 
ions are titrated with 
:
Step 4: Calculation of Permanent Hardness
Calculate the moles of 
equivalent to the 
used:
Convert moles of 
to moles of 
:
Moles of 
Moles of 
(since 1 mole of 
reacts with 
Calculate the mass of 
:
Mass of 
Moles of 
Molar mass of 
Convert mass of 
to ppm (parts per million) in the original 
of hard water:
(4) Final Calculation:
Given the steps involved, calculate the permanent hardness in ppm of 
using the above method.
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